The present invention is directed to automated analyzer systems and, more specifically, is directed to a retaining plate or disc used within a reactor of an automated analyzer system wherein the plate permits ingress or egress of a fluid stream through the reactor while retaining packing material within the reactor. A color development reactor in the detection system of an amino acid analyzer has been selected as a representative application.
In some amino acid analyzers, a very small or micro chromatographic column is used as a specialized application of a liquid column chromatographic separation technique, utilizing ion exchange resin as the stationary phase and eluting buffers of varying pH and salt concentration as the moving phase. Amino acids contained in a sample are introduced at the top of the column and are separated from each other as they are eluted through the resin bed which comprises the column packing. For amino acid analysis, the method for detecting the amino acids in the effluent stream has been to combine the column effluent with a reagent that is metered into the stream at a flow rate proportionally to that of the column eluent. When the reagent combines with the amino acids present in the stream, compounds are formed which, when subjected to further development process, can be detected by specific changes in optical properties such as absorption or fluorescence.
One of the classical detection methods in amino acid analyzer systems is that developed by Spackman and Moore, wherein the reagent used is ninhydrin dissolved in a suitable solvent/buffer solution. Under this process, the column effluent/reagent solution is heated in a reactor to a fixed temperature for a specified period of time. The compound developed as a result of this process will have specific colors, the intensities of which are proportional to the amounts of compounds contained in the flowing stream. The optical density of these compounds is measured at specific wavelengths.
Important to the calibration of the analyzer in terms of its specific sensitivity to detect amino acids is that the fluid/reagent mixture be maintained at a constant elevated temperature for a fixed period of time. It is critical to the stability of the instrument calibration that the two parameters of temperature and exposure time remain constant during the color development process. Classically, this has been accomplished by causing the effluent to pass through a TFE Teflon capillary coil which is normally suspended in a boiling water bath to act as the reactor in the amino acid analyzer system.
The separation techniques employed in early analyzers required several hours to complete a single analysis. In such systems, it became common practice to retain the flowing stream within the reactor for as long as fifteen minutes to complete the color development. Newer techniques have increased the performance of these analyzers to permit the same analyses to be completed in the order of twenty minutes. It has then become necessary to provide increased color development in a much shorter period of time. Reference is made to FIG. 1 showing empirical results of studies which relate the optical densities of compounds formed by mixtures of ninhydrin and amino acids as a function of development time and temperature.
Although many prior arrangements have used the design of TFE Teflon capillaries immersed in boiling water to obtain the necessary reactor temperatures, more recent approaches have envisioned the use of an elongated straight tube or column which is packed with inert material having a small particle size. This reactor tube can be heated by a variety of approaches, including placing the reactor on a thermoconductive block to which is attached a thermoelectric module, which operates in conjunction with a heat sink. By proper control of the operation of the thermoelectric module, the reactor can operate significantly above 100.degree. C. without damage to the apparatus or the stream being analyzed. The temperature control apparatus for the reactor using a thermoelectric module can maintain a temperature as high as 150.degree. C. with a capability of controlled cooling, as well as rapid cooldown in the case of power loss to the system.
One of the necessary elements in a reactor that is packed with small inert material such as diamond particles (approximately 0.002 inch diameter) is a retaining plate or disc positioned at each end of the reactor to properly retain the extremely small particles within the reactor while allowing for the requisite flow of the stream in and out of the reactor. The retention of the particles within the reactor is very important, since it is necessary for the successful operation of the analyzer to avoid any excess voids or space in the diamond packing. One approach in the design of a retaining plate used in a reactor for an amino acid analyzer has been to perforate the plate with a plurality of possibly six or eight holes each having a diameter of less than 0.002 inches. Because of the corrosive content of the stream flowing through the analytical system, platinum has been used for the plate having a thickness of approximately 0.003 inches. Consequently, it is exceedingly difficult and expensive to place the necessary number of holes with the critical diameter in the thin platinum plate.
One concern with respect to the use of a plurality of single holes in a thin disc or plate is possible occurrences of plugging of these holes which could result in serious problems, since the system is operating at high pressure and could result in damage to pressure gauges.
Another problem with respect to utilizing a plurality of single holes in the plate is the fact that holes any smaller than 0.002 inches in diameter may accentuate the reactor plugging problem. However, it is desirable to use particles in the packing of the reactor having a size no larger than 80 microns. Within limits, smaller sizes will improve the instrument resolution.
Although one approach to possible solution for reactor plugging is to place many more holes in the retaining plate, the cost of piercing additional holes in a thin plate made of a material such as platinum is high.